This invention relates to a system for linearizing a non-linear output produced as a function of a parameter of interest and which employs second slope data for carrying out the linearization.
Analog voltage to digital count conversion techniques are frequently used to obtain digital data representing non-linear curves or functions obtained in certain meeasurements. For example, these techniques may be employed to measure the voltage, in digital form, of a thermocouple, which has a non-linear temperature-voltage function. In order to obtain a true measure of temperature, however, the digital data must be "linearized", i.e., it must be made proportional to the temperature rather than to the voltage.
A popular method of linearization involves establishing a gating signal that is proportional in time duration to the voltage measured. This gating signal is used to pass pulses from a clock generator to a pulse counter. To achieve linearization, the frequency of these pulses is modified and made proportional to the average voltage slope over each of a plurality of segments into which the temperature-voltage curve is divided. Thus within each segment, the output frequency of the pulses will be constant and proportional to the average slope of the corresponding segment. The resulting pulses are accumulated for each measurement for display purposes. The resultant measurement, when obtained over the full range of the thermocouple, results in a broken approximation of the temperature-voltage curve made up of straight lines, one straight line for each segment.
This linearization technique has disadvantages in that it inherently produces significant errors at the ends and/or midpoints of each segment if the temperature-voltage function is not a straight line.